Reversible and irreversible variation of the superstructure of highly oriented low-density polyethylene during heat treatment

The small-angle x-ray scattering (SAXS) intensity of highly-oriented, low-density polyethylene (LDPE) with fixed draw ratio has been investigated during several heating and cooling cycles. Using a three-dimensional, monoclinic, paracrystalline superlattice to describe the superstructure of the sample, it has been possible to calculate the SAXS patterns completely. A very large irreversible variation of the superstructure during the first heating cycle, and a smaller reversible variation of the average size and distance of the crystallites during subsequent temperature cycles, could be obtained. These results can be explained using the thermodynamic theory of crystallization of polymer multicomponent systems of Kilian.     

Synthesis and characterization of novel spirooxazacamphorsultam derivatives

Derivatives of camphorsultam which contain novel spirooxazolidine and spirooxazine structures have been prepared in high yield and purity. Though it was expected that the ketone moiety would undergo acetal formation, the imine instead underwent reaction and was proven by X-ray crystallography and 2D NMR techniques. The initial ketone-containing derivatives were then reduced to produce exo-hydroxy analogs that have potential as a new family of chiral auxiliaries.     

Convergence to equilibrium for the Cahn–Hilliard equation with a logarithmic free energy

In this paper we investigate the asymptotic behavior of the nonlinear Cahn–Hilliard equation with a logarithmic free energy and similar singular free energies. We prove an existence and uniqueness result with the help of monotone operator methods, which differs from the known proofs based on approximation by smooth potentials. Moreover, we apply the Lojasiewicz–Simon inequality to show that each solution converges to a steady state as time tends to infinity.     

Die Adsorption als Vorstufe der chemischen Verbindung,untersuchtdurch Adsorptionsmessungen am Zirkonoxydhydrogel. II

Ohne Zusammenfassung     

Direct In Situ Investigation of Milling Reactions Using Combined X‐ray Diffraction and Raman Spectroscopy

The combination of two analytical methods including time‐resolved in situ X‐ray diffraction (XRD) and Raman spectroscopy provides a new opportunity for a detailed analysis of the key mechanisms of milling reactions. To prove the general applicability of our setup, we investigated the mechanochemical synthesis of four archetypical model compounds, ranging from 3D frameworks through layered structures to organic molecular compounds. The reaction mechanism for each model compound could be elucidated. The results clearly show the unique advantage of the combination of XRD and Raman spectroscopy because of the different information content and dynamic range of both individual methods. The specific combination allows to study milling processes comprehensively on the level of the molecular and crystalline structures and thus obtaining reliable data for mechanistic studies.     

Aluminum foils: the contrasting characters of hyperconjugation and steric repulsion in aluminum dimetallocenes

The novel sandwich complex Cp2*Al2I2, which was recently synthesized by Minasian and Arnold, has been characterized using ab initio and density functional methods. A large family of related compounds was also investigated. Although a few Al(II)–Al(II) bonds are known, this is the first such bond to be supported by Cp-type ligands. In addition, in the remarkable Cp4*Al4 synthesis by Roesky, Cp2*Al2I2 is the Al(II) intermediate; Cp4*Al4 is important as a precursor to novel organoaluminum species. Halogen and ligand effects on the Al–Al bond in Cp2*Al2I2 were systematically explored by studying a series of 20 Cp2*Al2I2 derivatives using density functional theory with relativistic basis sets for the halogens. Comparison was made with the focal point treatment, which uses extrapolation to estimate the full configuration interaction and complete basis set limit energy. Torsional potential energy curves, natural population analyses, and enthalpies of hydrogenation were computed. Using the focal point approach, torsional barriers were computed with 0.05 kcal mol(–1) uncertainty. The interplay of steric and electronic effects on the torsional potential energy curves, enthalpies of dehydrogenation reactions, and geometries is discussed. In species with small ligands (R = H, Me), hyperconjugative effects determine the torsional landscape, whereas steric repulsions dominate in species with Cp* alkyl ligands. Species with Cp ligands represent an intermediate case, thus providing insight into how ligands modulate the structures and properties of small metal clusters.     

Aftershocks in coherent-noise models

The decay pattern of aftershocks in the so-called ‘coherent-noise’ models [M.E.J. Newman, K. Sneppen, Phys. Rev. E 54 (1996) 6226] is studied in detail. Analytical and numerical results show that the probability to find a large event at time t after an initial major event decreases as t^−τ for small t, with the exponent τ ranging from 0 to values well above 1. This is in contrast to Sneppen and Newman, who stated that the exponent is about 1, independent of the microscopic details of the simulation. Numerical simulations of an extended model [C. Wilke, T. Martinetz, Phys. Rev. E 56 (1997) 7128] show that the power-law is only a generic feature of the original dynamics and does not necessarily appear in a more general context. Finally, the implications of the results to the modelling of earthquakes are discussed.     

Experimental Study of Nonlinear Behaviour of a Neon Glow Discharge

We report on experimental investigations of a periodically perturbed Neon glow discharge in a parameter range where the unperturbed system is characterized by the existence of p- and r- waves. Though the experimental plasma system has many potential degrees of freedom, its phase space behaviour is low dimensional. The discharge current exhibits sequences of periodic, quasi-periodic and chaotic states which in many aspects correspond to a dissipative circle map. Moreover experiments show that the system displays a route to chaos via formation of entrainment islands and subsequent folding and break up of the tori, which cannot be described by a one-dimensional theory, and which has not been reported in the literature until now.